Dear Lucy,
You might consider some of the scale construction techniques
available in the psych package. In particular, the iclust function
is meant for this very problem: how to form reliable item composites.
Bill
At 4:38 PM +0100 4/12/11, Christian Hennig wrote:
Dear Lucy,
not an R-related response at all, but if it's questionnaire data,
I'd probably try to do dimension reduction in a non-automated way by
defining a number of 10 or so meaningful scores that summarise your
questions.
Dimension reduction is essentially about how to aggregate the given
information into low-dimensional measurements, which according to my
opinion should be rather driven by the research aim and meaning of
the variables than by the distribution of the data, if at all
possible.
You can then use PCA in order to examine the remaining dimensions
Christian
On Tue, 12 Apr 2011, Lucy Asher wrote:
First of all I should say this email is more of a general
statistics questions rather than being specific to using R but I'm
hoping that this may be of general interest.
I have a dataset that I would really like to use PCA on and have
been using the package pcaMethods to examine my data. The results
using traditional PCA come out really nicely. The dataset is
comprised of a set of questions on dog behaviour answered by their
handlers. The questions fall into distinct components which may
biological sense and the residuals are reasonable small. Now the
problem. I don't have a big enough sample to run traditional PCA. I
have about 40 dogs and 60 questions so which ever way you look at
it not enough. There is past data available on some of the
questions and the realtionships between them so I was wondering
whether Bayesian PCA would be a useful alternative using past
research to inform my priors. I wondered if anyone knew whether
Bayesian PCA was better suited to smaller datasets than traditional
(ML) PCA? If not I wondered if anyone knew of packages in R that
could do dimension reduction on datasets with small sample sizes?
Many Thanks,
Lucy
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University College London, Department of Statistical Science
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Professor http://personality-project.org
Department of Psychology http://www.wcas.northwestern.edu/psych/
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